Applying adhesive stream of epoxy resin, rubber modified epoxy resin and capped isocyanate prepolymer

ABSTRACT

The invention is a composition comprising applying to a substrate a stream of an adhesive comprising:
     one or more epoxy resins;   one or more rubber modified epoxy resins;   one or more toughening compositions comprising the reaction product of one or more isocyanate terminated prepolymers and one or more capping compounds having one or more phenolic, benzyl alcohol, aminophenyl, or, benzylamino groups wherein the reaction product is terminated with the capping compounds;   one or more curing agents for epoxy resins and one or more catalysts which initiate cure at a temperature of about 100° C. or greater; and   optionally; fillers adhesion promoters, wetting agents or rheological additives useful in epoxy adhesive compositions;   wherein the adhesive composition has a viscosity at 45° C. of about 20 Pa·s to about 400 Pa.s. The composition can be used as an adhesive and applied as a stream using a high speed streaming process.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Divisional of prior application Ser. No.10/886,109 filed Jul. 7, 2004 abandoned. This application claims thebenefit of U.S. Provisional application No. 60/485,284, filed Jul. 7,2003.

BACKGROUND OF INVENTION

This invention relates to an epoxy based adhesive containing atoughening agent and a method of applying such adhesive using astreaming process.

Epoxy resin based adhesives are used to bond a variety of differentsubstrates together. In the automotive industry, epoxy resin adhesivesare used to bond certain parts together, and are known as structuraladhesives. A structural adhesive is an adhesive which bonds parts of thebody structure of an automobile together. The problem with epoxy resinsas used in adhesive compositions is that the epoxy resins are somewhatbrittle and subject to fracturing when impacted. This tendency tofracture can be reduced by the addition of toughening agents. Theproblem with the use of toughening agents is that such toughening agentstend to increase the viscosity of the composition and the increasedviscosity limits the method and speed of application. Mülhaupt, U.S.Pat. No. 5,278,257 discloses an epoxy resin containing (a) copolymerbased on at least one 1,3-diene and at least one polar, ethylenicallyunsaturated comonomer and (b) a phenol-terminated polyurethane, polyureaor polyurea urethane. The adhesives disclosed in Mülhaupt are excellentstructural adhesives. Because these adhesives are very viscous, they arenot useful in some high-volume applications which require highapplication speeds.

In particular these materials are applied generally as an extruded beaddirectly on the surface and have a viscosity of from about 150 to about600 Pa·s. measured at 45° C. In another application these adhesives areapplied using swirl techniques at a viscosity of about 100 Pa·s. Theprocess of applying an adhesive using an extruded bead is too slow formany high speed applications. The swirl process is a faster applicationbut is not ideal for high-volume structural applications.

What is needed is a process for applying structural adhesives based onepoxy resins wherein the adhesive can be applied fast and inhigh-volume.

SUMMARY OF INVENTION

The invention is a method of applying an adhesive composition comprisingapplying to a substrate a stream of an adhesive comprising:

-   -   A) one or more epoxy resin;    -   B) one or more rubber modified epoxy resins;    -   C) one or more toughening compositions comprising the reaction        product of one or more isocyanate terminated prepolymers and one        or more capping compounds having one or more bisphenolic,        phenolic, benzyl alcohol, aminophenyl or, benzylamino moieties        wherein the reaction product is terminated with the capping        compounds;    -   D) one or more curing agents and one or more catalysts for epoxy        resins which initiates cure at a temperature of about 100° C. or        greater; and    -   E) optionally; fillers, adhesion promoters, wetting agents or        rheological additives useful in epoxy adhesive compositions;        wherein the adhesive composition has a viscosity at 45° C. of        about 20 Pa·s to about 400 Pa·s. preferably 20 to about 150        Pa·s. The isocyanate terminated prepolymer is the reaction        product of an aliphatic polyisocyanate and a hydroxyl or amine        terminated polyether wherein the polyether may contain urea or        urethane linkages in the backbone. The capping compound        comprises one or more aromatic or bisaromatic rings with one or        more hydroxyl, amino, methyl amine or methylol groups attached        to one or more of the aromatic rings. Where the capping compound        contains more than one aromatic ring, the aromatic rings are        bonded together through a carbon to carbon bond between two        carbons on the aromatic rings, an alkylene, oxygen, carbonyl,        carbonyloxy, or amido group and the aromatic rings may further        be substituted with one or more alkyl, amino, alkylamino and/or        hydroxyl groups provided such group does not interfere with the        reaction of hydroxyl and/or amino groups with isocyanate groups.        The reaction product has a crosslinking density such that the        viscosity of the reaction product is as described herein at 45°        C.

Further the invention is a method of applying the adhesive compositionby applying it to a substrate in the form of a stream of the adhesive.This can performed using a high speed streaming apparatus.

The streamable adhesive can be applied at a speed of about 200 to about400 millimeters (mm) per second. The adhesive used in the invention canbe formulated to have relatively low viscosity yet provide a highstrength bond.

DETAILED DESCRIPTION OF INVENTION

The toughening agents comprise the reaction product of one or moreisocyanate terminated prepolymers with one or more capping agents,wherein the isocyanate used to prepare the prepolymer has aliphaticand/or cycloaliphatic groups. Preferably, the prepolymer has a molecularweight so as to result in a low viscosity adhesive composition.Preferably, the viscosity of the prepolymer is from about 20 Pa·s. orgreater, more preferably about 100 Pa·s. or greater. Preferably, theprepolymer has a viscosity of about 1000 Pa·s. or less and morepreferably about 800 Pa·s. or less. In order to achieve the desiredviscosity of the toughening agent, the number of branches of theisocyanate prepolymer and the crosslink density of the ultimate reactionproduct must be kept low. The number of branches of the prepolymer isdirectly related to the functionality of the raw materials used toprepare the isocyanate terminated prepolymer. Functionality refers tothe number of reactive groups in the reactants. Preferably the number ofbranches in the prepolymer is about 6 or less and more preferably about4 or less. Preferably the number of branches is about 1 or greater andmore preferably about 2 or greater. Crosslink density is the number ofattachments between chains of polymers. At higher crosslink densitiesthe viscosity of the reaction product is higher. The crosslink densityis impacted by the functionality of the prepolymer and by the processconditions. If the temperature of the reaction to prepare the tougheningagent is kept relatively low, crosslinking can be minimized. Preferablythe crosslink density is about 2 or less and more preferably about 1 orless. Preferably, the molecular weight of the prepolymer is about 8,000(Mw) or greater, and more preferably about 15,000 (Mw) or greater.Preferably, the molecular weight of the prepolymer is about 40,000 (Mw)or less, and more preferably about 30,000 (Mw) or less. Molecularweights as used herein are weight average molecular weights determinedaccording to GPC analysis. The amount of capping agent reacted with theprepolymer should be sufficient to cap substantially all of the terminalisocyanate groups. What is meant by capping the terminal isocyanategroups with a capping agent is that the capping agent reacts with theisocyanate to place the capping agent on the end of the polymer. What ismeant by substantially all is that a minor amount of free isocyanategroups are left in the prepolymer. A minor amount means an amount of thereferenced feature or ingredient is present which does not impact in anysignificant way the properties of the composition. Preferably, the ratioof capping agent equivalents to isocyanate prepolymer equivalents isabout 1:1 or greater, more preferably about 1.5:1 or greater.Preferably, the equivalents ratio of capping agent to isocyanate ofprepolymer is about 2.5:1 or less and more preferably about 2:1 or less.

Preferably, the reaction product corresponds to one of the formulas I orII:

-   R¹ is independently in each occurrence a C₂₋₂₀ m-valent alkyl    moiety;-   R² is independently in each occurrence a polyether chain;-   R³ is independently in each occurrence an alkylene, cycloalkylene or    mixed alkylene and cycloalkylene moiety, optionally containing one    or more oxygen or sulfur atoms;-   R⁴ is a direct bond or an alkylene, carbonyl, oxygen, carboxyloxy,    or amido moiety;-   R⁵ is independently in each occurrence an alkyl, alkenyl, alkoxy,    aryloxy or aryloxy moiety with the proviso that if p=1, then q=0;-   X is O or —NR⁶ with the proviso that X is O where p is 1; and that    where p is 0, X is O in at least one occurrence;-   R⁶ is independently in each occurrence hydrogen or alkyl;-   m is independently in each occurrence a number of about 1 to about    6;-   n is independently in each occurrence a number of 1 or greater;-   o is independently in each occurrence 0 or 1 if p is 0 and 0 if p is    1;-   p is independently in each occurrence 0, or 1; and-   q is independently in each occurrence a number of from 0 to 1.

The isocyanate terminated prepolymer corresponds to one of formulas IIIand IV

and capping compound corresponds to formula V

wherein R¹, R², R³, R⁴, R⁵, m, n, o, p and q are as definedhereinbefore.

R⁴ is preferably a direct bond or an alkylene, oxygen, carbonyl,carbonyloxy, or amido moiety. More preferably, R⁴ is a direct bond or aC₁₋₃ straight or branched alkylene moiety.

Preferably R⁵ is independently in each occurrence an alkyl, alkenyl,alkyloxy or aryloxy moiety with the proviso that if p=1 then q=0. Morepreferably R⁵ is a C₁₋₂₀ alkyl, C₁₋₂₀ alkenyl, C₁₋₂₀ alkoxy or C₆₋₂₀aryloxy moiety. More preferably, R⁵ is a C₃₋₁₅ alkyl or C₂₋₁₅ alkenylmoiety.

Preferably, o is 0. Preferably, N is independently in each occurrenceabout 1 to about 3.

The polyether polyol or polyamine used to prepare the isocyanateterminated prepolymer of formula (III) can be any conventional polyetherpolyamine or polyol known to those skilled in the art. In order toprepare the prepolymer, the polyether polyol or polyether polyamine isreacted with an equivalents excess of a polyisocyanate in the presenceof a polyaddition catalyst under conditions such that the hydroxyl oramino groups react with the polyisocyanate to form an isocyanatefunctional adduct of formula (III). If the starting compound is apolyether having two or more amino groups the prepolymer contains ureagroups. If it is a polyether polyol the resulting prepolymer containsurethane groups. In order to produce the prepolymer of formula (IV) thestarting compound is a C₂₋₂₀ mono or poly alcohol or amine. In this casethe starting compound is reacted with a polyether polyol or a polyetherpolyamine and an equivalents excess of a polyisocyanate in the presenceof a polyaddition catalyst under conditions such that an isocyanatefunctional prepolymer is prepared. Conventional polyaddition conditionsare used for this reaction step. In prepolymer preparation, an excess ofthe polyisocyanate is reacted with the polyether polyol or polyamine soas to provide or result in the preparation of an isocyanate functionalprepolymer. Preferably, the equivalent ratio of polyisocyanate withrespect to the total of hydroxy and/or amino groups is about 1.5:1 orgreater and more preferably about 2:1 or greater. Preferably, theequivalent ratio is about 3.5:1 or less and more preferably about 3:1 orless.

The polyether polyols or polyamines useful in the invention is anypolyether or polyamine which can form a prepolymer with thepolyisocyanate and when capped with the phenol provides a prepolymerhaving the desired viscosity characteristics described hereinbefore. Thepolyether polyols or polyamines comprise a series of hydrocarbon groupsseparated by oxygen atoms and terminated with hydroxyl, or primary orsecondary amines (preferably primary amines). Preferably, R² is apolyalkylene polyether chain having a weight average molecular weight ofabout 400 to about 4,000. Preferably, the polyether is a polyalkyleneether, which is a series of alkylene groups alternating with oxygenatoms. Preferably, the polyalkylene polyether has a molecular weight ofabout 400 (Mw(weight average)) or greater, and more preferably about1000 (Mw) or greater. Preferably, the polyalkylene polyether has amolecular weight (Mw) of 8000 or less, and more preferably 3000 (Mw) orless. Polyalkylene as used in this context refers to a polyether havingrepeating units containing straight or branched chain alkylene groups.Preferably, the alkylene group is from 2 to about 6 carbons, and can bestraight or branched chain, more preferably from about 2 to about 4carbon atoms and most preferably 3 to about 4 carbon atoms. Preferably,the alkylene groups are derived from ethylene oxide, propylene oxide,butylene oxide or tetrahydrofuran. Preferably, the polyether polyols orpolyamines which are used to prepare the prepolymer have a functionalityof about 2 to about 6, more preferably about 2 to about 4, even morepreferably from about 2 to about 3 and most preferably about 2. Thepolyether polyols or polyamines may also contain the residue of aninitiator compound used to initiate polymerization of the alkylene oxideor tetrahydrofuran to make the polyalkylene polyether via techniquesknown to those skilled in the art. In a preferred embodiment thepolyether is derived from tetrahydrofuran.

In the formulas used herein R² represents the residue of a polyethersegment of the polymers represented. As used herein residue means thatthe polyether remaining is that portion except for the end groups Xwhich are separately identified in the formulas (I) to (IV).

The polyether residue preferably has a molecular weight (weight average)of about 400 or greater, more preferably about 1000 or greater and mostpreferably about 1500 or greater. The polyether residue preferably has amolecular weight of about 8000 or less, more preferably about 6000 orless and most preferably about 3000 or less.

Starting compounds which are useful to produce prepolymers of theformula II in this invention are compounds having about 1 to about 8,preferably about 2 to about 8, more preferably about 2 to about 4, mostpreferably about 2 to about 3 active hydrogens. Preferable startingcompounds include, for example, alcohols, glycols, low molecular weightpolyols, glycerin, trimethylol propane, pentaerythritol, glucosides,sugars, ethylene diamine, diethylene triamine, and the like.Particularly, suitable glycols include ethylene glycol, 1,2-propyleneglycol, 1,3-propylene glycol, 1,2-butylene glycol, 1,3-butylene glycol,1,4-butylene glycol, 1,2-pentylene glycol, 1,3-pentylene glycol,1,4-pentylene glycol, 1,5-pentylene glycol, neopentyl glycol and varioushexane diols, mixtures thereof and the like. Preferred startingcompounds are trifunctional such as trimethylol propane.

In the formulas used herein, R¹ is the residue of a starting compound ora polyaddition initiator for the polyether, respectively, well known tothose skilled in the art. The starting compounds and initiators usefulherein preferably correspond to the formulaR¹(XH)_(m)wherein R¹, X and m are previously defined. Preferably the initiator ishydroxyl functional. Preferably R¹ is independently in each occurrence aC₂₋₂₀ m-valent alkyl group. More preferably R¹ is independently in eachoccurrence a C₂₋₈ m-valent alkyl group and even more preferably a C₂₋₆alkyl group. R¹ is independently in each occurrence a 2 to 6 valent,more preferably 2 to 4 valent and most preferably 2 to 3 valent.Preferably X is 0. Preferably, m is a number of about 2 to about 6, evenmore preferably a number of about 2 to about 4 and most preferably about2 to about 3.

The isocyanates useful in preparing the prepolymer and toughening agentof the invention include all aliphatic polyisocyanates. Aliphatic isused herein means that the isocyanate has in its backbone moieties whichare not aromatic, and preferably moieties of alkylene, cycloalkylene ora mixture thereof. Further, the aliphatic, such as alkylene and/orcycloalkylene, moieties may contain one or more oxygen or sulfur atoms.Poly is used herein means two or more. Polyisocyanates mean isocyanateswhich have on average two or more isocyanate groups. Preferably, theisocyanates are isocyanates having from about 2 to about 3 isocyanategroups on average and more preferably, on average, about 2 isocyanatemoieties. Preferred polyisocyanates correspond to the formulaR³

NCO)_(p)wherein R³ is as defined hereinbefore. Preferably, R³ is independentlyin each occurrence a C₁₋₂₀ alkylene, cycloalkylene or mixed alkylene andcycloalkylene moiety, optionally containing one or more oxygen or sulfuratoms in the alkylene and/or cycloalkylene chains. Mixed alkylene andcycloalkylene means a moiety that contains both straight and/or branchedchains and cyclic alkylene rings. More preferably, R³ is ethylene,trimethylene, tetramethylene, pentamethylene, hexamethylene,heptamethylene, octamethylene, decamethylene, dodecamethylene,tetradecamethylene, hexadecamethylene, octadecamethylene,eicosamethylene; moieties corresponding to the formulas:—(CH₂—CH₂—O)_(s)—CH₂—CH₂—,—(CH(CH₃—CH₂—O)_(s)—CH(CH₃)—CH₂—,—(CH₂—CH₂—CH₂—O)_(s)—CH₂—CH₂—CH₂—CH₂ and—CH₂—CH₂—S)_(s)—CH₂—CH₂—in which s is independently in each occurrence 1 to 20; orcyclopenthalene, cyclohexalene, cyclohepthalene or two or more of suchcycloalkylene groups bonded through a direct bond or bonded through analkylene group.

Among preferred isocyanates are ethylene diisocyanate, trimethylenediisocyanate, tetramethylene diisocyanate, pentamethylene diisocyanate,hexamethylene diisocyanate, heptamethylene diisocyanate, octamethylenediisocyanate, decamethylene diisocyanate, dodecamethylene diisocyanate,tetradecamethylene diisocyanate, hexadecamethylene diisocyanate,octadecamethylene diisocyanate, eicosamethylene diisocyanate,cyclohexamethylene diisocyanate, cyclopenthalene diisocyanate, orcyclohepthalene diisocyanate, or bis-cyclohexylene, cyclohexylmethylenediisocyanate, and the like. A most preferred isocyanate is hexamethylenediisocyanate.

The capping agent useful in this invention is any phenol, benzylalcohol, aromatic amine, or benzyl amine as described herein which isliquid or can be dissolved in the polyether used and which under definedreaction conditions herein reacts with the isocyanate groups of theprepolymer to cap the isocyanate groups.

Preferably, the capping agent is a phenol or a benzyl alcohol. In onepreferred embodiment the phenol is an alkyl substituted phenol andpreferably the alkyl group is a C₁₋₂₀ alkyl moiety, more preferablyC₂₋₁₅, alkyl moiety and most preferably a C₈₋₁₂ alkyl moiety.Preferably, the phenols correspond to the following formula

wherein R⁵ is more preferably a C₁₋₂₀ alkyl moiety, even more preferablya C₂₋₁₅ alkyl and most preferably a C₈₋₁₂ alkyl moiety. The size andlocation of the alkyl group on the phenol must not hinder or prevent thereaction of the hydroxyl group on the phenol with the isocyanatemoieties on the prepolymer. In another embodiment the phenol is abisphenol. The bisphenol is structured such that the two aromatic ringsare bonded to each other by a direct bond or through an alkylene,carboxyl, sulfinyl, sulfonyl or an alkyl substituted silane moiety.Preferably, the aromatic rings are bonded by a direct bond or analkylene moiety. Preferably, the alkylene moiety is C₁₋₂₀ straight orbranched chain, more preferably C₁₋₃ straight or branched chainalkylene. Preferably, the bisphenolic compound corresponds to theformula

wherein R⁴ is defined hereinbefore. Among preferred phenolic compoundsare bisphenol A, bisphenol F, 3-(n-penta-8′-decenyl)phenol ando-allylphenol.

The toughening agent is prepared according to the following process. Thefirst step is to determine whether the capping agent to be used is asolid or a liquid. If the capping agent to be used is a solid, it isdissolved in the polyether to be used. This process to dissolve thecapping agent can be performed at elevated temperatures, i.e.,temperatures necessary to dissolve the capping compound in thepolyether. Preferably, such temperatures are about 100° C. or greater,and most preferably 130° C. or greater, and preferably 150° C. or less,and most preferably 140° C. or less. If the capping agent is liquid, itis added later in the process.

The polyether with solid capping agent compound dissolved therein isthereafter contacted with the polyisocyanate in the presence of acatalyst suitable for catalyzing the reaction between hydroxyl groupsand isocyanate groups (a condensation catalyst). This contactinggenerally results in an exotherm. The capping agent and polyisocyanateare allowed to react until a prepolymer is formed which has isocyanatereactive moieties and substantially no hydroxyls present from thepolyalkylene polyether. Generally, an equivalent excess of isocyanate isused to achieve this. Preferably, an excess of isocyanate equivalents ofabout 0.5 or greater is preferred, more preferably about 1 or greater ismore preferred, and about 2.5 or less is preferred and more preferred isabout 2 or less. Generally, this reaction will take about 30 minutes ormore, more preferably about 60 minutes or more, preferably about 120minutes or less, and more preferably about 100 minutes or less.

This reaction is performed in the presence of a condensation catalyst.Examples of such catalysts include the stannous salts of carboxylicacids, such as stannous octoate, stannous oleate, stannous acetate, andstannous laureate; dialkyltin dicarboxylates, such as dibutyltindilaureate and dibutyltin diacetate; tertiary amines and tinmercaptides. Preferable condensation catalysts for this reaction aredibutyltin-dilaurate, tin-II-octoate and diazabicyclooctane. The amountof catalyst employed is generally between about 0.005 and about 5percent by weight of the mixture catalyzed, depending on the nature ofthe isocyanate. More preferably, the catalyst is used in an amount ofabout 0.002 percent by weight of the reaction mixture or more, mostpreferably about 0.01 percent by weight of the reaction mixture or more.More preferably, the catalyst is used in an amount of about 0.2 percentby weight of the reaction mixture or less, and most about 0.05 percentby weight of the reaction or less.

If the capping compound is dissolved in the polyether, it is importantto cool this reaction to keep the temperature below that temperature atwhich the prepolymer undergoes significant crosslinking. Preferably, thereaction mixture is cooled to a temperature of 90° C. or less, and morepreferably 80° C. or less. If the capping agent to be used is a liquidafter the completion of the reaction of the polyether with thepolyisocyanate has occurred, the reaction mixture is cooled to atemperature below that temperature at which significant crosslinkingcould occur, and the capping agent is added to the reaction mixture.Preferably, the reaction mixture is cooled to a temperature of about 90°C. or less, and more preferably about 80° C. or less. The capping agentand isocyanate functional prepolymer are reacted for a sufficient timeto cap the isocyanate moieties with the capping agent. Preferably, thisreaction continues for a period of about 20 minutes or greater, morepreferably about 50 minutes or greater, preferably the reaction iscontinued for a period about 120 minutes or less, and more preferablyabout 80 minutes or less. The catalyst from the previous step is presentso as to catalyze the reaction of this step. The resulting reactionmixture is thereafter useful to prepare an epoxy adhesive formulation.

One component of the adhesive composition is an epoxide resin, such asthose disclosed in U.S. Pat. No. 4,734,332, incorporated herein byreference, in particular column 2, line 66 to column 4, line 24. Epoxideresins which may be employed in the compositions of the invention arethose which contain groups illustrated in the following formula

wherein R⁸ is hydrogen or C₁₋₄ alkyl, preferably hydrogen or methyl andmost preferably hydrogen. Preferably, the epoxy resin is a rigid epoxyresin or a mixture of rigid epoxy resins and flexible epoxy resinswherein no more than 10 percent by weight of the epoxy resins include aflexible epoxy resin. As used herein, rigid epoxy resins refer to epoxyresins having bisphenol moieties in the backbone of the epoxy resin.Representative of preferred bisphenol resins useful in this inventionare those disclosed in U.S. Pat. No. 5,308,895 at column 8, line 6,incorporated herein by reference and represented by Formula 6.Preferably the rigid epoxy resin is a liquid epoxy resin or a mixture ofa solid epoxy resin dispersed in a liquid epoxy resin. The mostpreferred rigid epoxy resins are bisphenol-A based epoxy resins andbisphenol-F based epoxy resins.

Flexible epoxy resins as used herein refer to epoxy resins havingelastomeric chains in the backbone. Representative of such elastomericchains are polyether chains which are preferably prepared from one ormore alkylene oxides. Representative examples of these flexible epoxyresins are those described in U.S. Pat. No. 5,308,895 at column 8, line9 and formula 9 and the description thereof following, incorporatedherein by reference. Preferably the flexible epoxy resin contains in itsbackbone ethylene oxide, propylene oxide or a mixture thereof.

Another component is a rubber-modified epoxy resin. Preferably, theadhesive of the invention includes an epoxy-terminated adduct of anepoxy resin and a diene rubber or a conjugated diene/nitrile rubber.This adduct is suitably prepared in the reaction of a polyepoxide, acompound having an average of more than one epoxy group as describedhereinbefore, with a carboxy-functional conjugated diene rubber or aconjugated diene/nitrile rubber. The diene rubber is a polymer of aconjugated diene monomer such as butadiene and isoprene. Butadienerubbers are preferred. Conjugated diene/nitrile rubbers are copolymersof a conjugated diene and an ethylenically unsaturated nitrile monomer,of which acrylonitrile is the most preferred one. When a conjugateddiene/nitrile rubber is used, at least one such rubber present in thecomposition contains less than about 30 weight percent polymerizedunsaturated nitrile, and preferably no more than about 26 weight percentpolymerized unsaturated nitrile. The rubber also contains terminalgroups that will react with an epoxide to form a covalent bond thereto.Preferably, the rubber contains from about 1.5, more preferably fromabout 1.8, to about 2.5, more preferably to about 2.2, of such terminalgroups per molecule, on average. Carboxyl-terminated rubbers arepreferred. The rubber is preferably a liquid at room temperature, andpreferably has a glass transition temperature of less than about −25°C., preferably from about −30 to about −90° C. The molecular weight(M_(n)) of the rubber is suitably from about 2000 to about 6000, morepreferably from about 3000 to about 5000. Suitable carboxyl-functionalbutadiene and butadiene/acrylonitrile rubbers are commercially availablefrom Noveon under the tradenames Hycar® 2000X162 carboxyl-terminatedbutadiene homopolymer and Hycar® 1300X31 carboxyl-terminatedbutadiene/acrylonitrile copolymer. A suitable amine-terminatedbutadiene/acrylonitrile copolymer is sold under the tradename Hycar®1300X21. Examples of nitrile rubbers are Hycar® 1300X8, Hycar® 1300X13,Hycar® 1300X9, Hycar® 1300X18 and Hycar® 1300X31 carboxyl-terminatedbutadiene acrylonitrile copolymers, all commercially available fromNoveon.

The conjugated diene or conjugated diene/nitrile rubber is formed intoan epoxy-terminated adduct by reaction with an excess of a polyepoxide.A wide variety of polyepoxide compounds such as cycloaliphatic epoxides,epoxidized novolac resins, epoxidized bisphenol A or bisphenol F resins,butanediol polyglycidyl ether, neopentyl glycol polyglycidyl ether orflexible epoxy resins can be used, but generally preferred on the basisof cost and availability are liquid or solid glycidyl ethers of abisphenol such as bisphenol A or bisphenol F. Halogenated, particularlybrominated, resins can be used to impart flame retardant properties ifdesired. For forming the adduct, liquid epoxy resins (such as BisphenolA-based epoxy resin, DER 331, available from The Dow Chemical Company)are especially preferred for ease of handling in making the adduct.Typically, the rubber and an excess of the polyepoxide are mixedtogether with a polymerization catalyst such as a substituted urea orphosphine catalyst, and heated to a temperature of about 100 to about250° C. in order to form the adduct. Preferred catalysts include phenyldimethyl urea and triphenyl phosphine. Preferably, enough of thepolyepoxide compound is used that the resulting product is a mixture ofthe adduct and free polyepoxide compound.

The epoxy adhesive composition further contains a heat-activated curingagent. Preferably, that heat-activated curing agent is anitrogen-containing heat-activated curing agent sometimes referred to asa latent curing agent. The curing agent (b) used in the new compositionsmay be any substance that remains inert towards epoxide resins below acertain “threshold” temperature, which is usually at least about 80° C.,and preferably at least about 100° C. or above, but reacts rapidly toeffect curing once that threshold temperature has been exceeded. Suchmaterials are well known and commercially available and include borontrichloride/amine and boron trifluoride/amine complexes, dicyandiamide,melamine, diallylmelamine, guanamines such as acetoguanamine andbenzoguanamine, aminotriazoles such as 3-amino-1,2,4-triazole,hydrazides such as adipic dihydrazide, stearic dihydrazide, isophthalicdihydrazide, semicarbazide, cyanoacetamide, and aromatic polyamines suchas diaminodiphenylsulphones. The use of dicyandiamide, isophthalic aciddihydrazide, adipic acid dihydrazide and 4,4′-diaminodiphenylsulphone isparticularly preferred.

The adhesive composition useful in the invention can further containother additives that are common in the adhesive art. Other customaryadditives which the mixtures according to the invention can contain areplasticizers, extenders, fillers and reinforcing agents, for example,coal tar, bitumen, textile fibers, glass fibers, asbestos fibers, boronfibers, carbon fibers, mineral silicates, mica, powdered quartz,hydrated aluminum oxide, bentonite, wollastonite, kaolin, silica aerogelor metal powders, for example, aluminum powder or iron powder, and alsopigments and dyes, such as carbon black, oxide colors and titaniumdioxide, fire-retarding agents, thixotropic agents, flow control agents,such as silicones, waxes and stearates, which can, in part, also be usedas mold release agents, adhesion promoters, antioxidants and lightstabilizers.

The epoxy resin or epoxide resin used in the invention is used insufficient amount to give the desired adhesive and strength properties.Preferably, the epoxy resin is used in an amount of about 30 parts perhundred parts of adhesive composition or greater, more preferably about40 parts per hundred parts of the adhesive composition or greater, andmost preferably about 50 parts per hundred parts of adhesive compositionor greater. The epoxy resin is preferably used in the amount of about 80parts per hundred parts of adhesive composition or less, more preferablyabout 70 parts of epoxy resin per hundred parts of adhesive compositionor less, and most preferably about 60 parts per hundred parts ofadhesive composition or less.

Preferably the rubber-modified epoxy resins are used in an amount ofabout 0 parts per hundred parts of adhesive composition or greater, andmore preferably about 5 parts per hundred parts of adhesive compositionor greater, and most preferably about 10 parts per hundred parts ofadhesive composition or greater. The rubber-modified epoxy resin is usedin about 25 parts per hundred parts of adhesive composition or less,more preferably about 20 parts per hundred parts of adhesive compositionor less, and more preferably about 15 parts per hundred of adhesivecompositions or less. The curing agent is used in sufficient amount tocure the composition. Preferably, the curing agent is used in an amountof about 0 parts per hundred parts of adhesive composition or greater,more preferably about 3 parts per hundred parts of adhesive compositionor greater, and most preferably about 5 parts per hundred parts ofadhesive composition or greater. The curing agent is preferably used inamount of about 15 parts per hundred parts of adhesive composition orless, more preferably about 10 parts per hundred parts of adhesivecomposition or less, and most preferably about 8 parts per hundred partsof adhesive composition or less.

Fillers are used in sufficient amount to provide the desired rheologicalproperties. Preferable fillers are used in an amount of about 0 partsper hundred parts of adhesive composition or greater, more preferablyabout 5 parts per hundred parts of adhesive composition or greater, andmost preferably about 10 parts per hundred parts of adhesive compositionor greater. The fillers are present in an amount of about 25 parts perhundred parts of adhesive composition or less, more preferably about 20parts per hundred parts of adhesive composition or less, and mostpreferably about 15 parts per hundred parts of adhesive composition orless.

The toughening agent is present in sufficient amount to improve theperformance of adhesive compositions containing it under dynamic load.Preferably, the toughening agents of the invention are present in anamount of about 5 parts per hundred parts of adhesive composition orgreater, preferably about 7 parts per hundred parts of adhesivecomposition or greater and most preferably about 10 parts per hundredparts of adhesive composition or greater. Preferably, the tougheningagent is present in an amount of about 35 parts per hundred parts ofadhesive composition or less, preferably about 25 parts per hundredparts of adhesive composition or less and more preferably about 20 partsper hundred parts of adhesive composition or less.

The adhesive composition further comprises a catalyst for the cure ofthe reaction. Any suitable catalyst for an epoxy curing reaction may beused. Epoxy catalysts are present in sufficient amount to catalyze thecuring reaction when exposed to temperatures at which the latent curingagent begins the cure. Among preferred epoxy catalysts are ureas such asp-chlorophenyl-N,N-dimethylurea (Monuron), 3-phenyl-1,1-dimethylurea(Phenuron), 3,4-dichlorophenyl-N,N-dimethylurea (Diuron),N-(3-chloro-4-methylphenyl)-N′,N′-dimethylurea (Chlortoluron),tert-acryl- or alkylene amines like benzyldimethylamine,2,4,6-tris(dimethylaminomethyl)phenol, piperidine or derivates thereof,imidazole derivates, in general C₁-C₁₂ alkylene imidazole orN-arylimidazols, such as 2-ethyl-2-methylimidazol, or N-butylimidazol,6-caprolactam, a preferred catalyst is2,4,6-tris(dimethylaminomethyl)phenol integrated into apoly(p-vinylphenol) matrix (as described in European patent EP 0 197892). Preferably, the catalyst is present in the adhesive composition inthe amount of about 0 parts per hundred parts of adhesive composition orgreater, more preferably about 0.3 parts per hundred parts of adhesivecomposition or greater, and most preferably about 0.5 parts per hundredparts of adhesive composition or greater. Preferably, the epoxy curingcatalyst is present in an amount of about 2 parts per hundred parts ofadhesive composition or less, more preferably about 1.5 compositionparts per hundred parts of adhesive or less, and most preferably about1.3 parts per hundred parts of adhesive composition or less.

Preferably, the adhesive composition has a viscosity of about 150 Pa·sor less, more preferably about 100 Pa·s or less at 45° C. Preferably,the compositions have a viscosity of about 20 Pa·s. or greater at 45°C., and most preferably about 30 Pa·s. or greater at 45° C.

The adhesive composition can be applied by any techniques well known inthe art. It can be applied by extruding it from a robot into bead formon the substrate, it can be applied using mechanical application methodssuch as a caulking gun, or any other manual application means, it canalso be applied using a swirl technique. The swirl technique is appliedusing an apparatus well known to one skilled in the art such as pumps,control systems, dosing gun assemblies, remote dosing devices andapplication guns. Preferably, the adhesive is applied to the substrateusing a streaming process. What is meant by applying by a streamingprocess means spraying a bead at a distance, nozzle to substrate, ofabout 3 to about 10 mm, using pressures of about 50 to about 300 bar,speeds of about 200 to about 500 mm/s, application temperatures fromabout 20° C. to about 65° C. and nozzle diameter of about 0.5 to about1.5 mm. Equipment known to those skilled in art can be used for applyingthe adhesive via a steaming process and include pumps, control systems,dosing gun assemblies, remote dosing devices and application guns.Generally, the adhesive is applied to one or both substrates. Thesubstrates are contacted such that the adhesive is located between thesubstrates to be bonded together. Thereafter, the adhesive compositionis subjected to heating to a temperature at which the heat curable orlatent curing agent initiates cure of the epoxy resin composition.Generally, this temperature is about 80° C. or above, more preferablyabout 100° C. or above. Preferably, the temperature is about 220° C. orless, and more preferably about 180° C. or less.

The adhesive of the invention can be used to bond a variety ofsubstrates together including wood, metal, coated metal, aluminum, avariety of plastic and filled plastic substrates, fiberglass and thelike. In one preferred embodiment, the adhesive is used to bond parts ofautomobiles together or parts to automobiles. Such parts can be steel,coated steel, aluminum, coated aluminum, plastic and filled plasticsubstrates.

The adhesive composition once cured preferably has an e-modulus of about1200 MPa as measured according to the following tests. Preferably thee-modulus is about 1400 MPa or greater. Preferably, the cured adhesivedemonstrates a tensile strength of about 30 MPa or greater, morepreferably about 35 MPa or greater, and most preferably about 40 MPa orgreater. Preferably, the adhesive demonstrates an elongation of about 3percent or greater, more preferably about 5 percent or greater, and mostpreferably about 9 percent or greater as measured according to DIN ENISO 527-1. Preferably, the yield point at 45° C. is about 200 Pa. orgreater, more preferably about 250 Pa. or greater, and most preferablyabout 300 Pa. or greater measured on a Bohlin viscosimeter andcalculated after Casson. Preferably, the lap shear strength of a 1.5 mmthick cured adhesive layer is about 15 MPa or greater, more preferablyabout 20 MPa or greater, and most preferably about 25 MPa or greatermeasured according to DIN EN 1465. Preferably, the impact peel strengthat room temperature of the cured adhesive is about 15 N/mm or greater,more preferably about 20 N/mm or greater, and most preferably about 30N/mm or greater measured according to ISO 11343.

Molecular weights as quoted herein are weight average molecular weightsmeasured according to GPC analysis using mixed polystyrene as columnmaterial, THF as diluent and linear polystyrene as standard at 45° C.

EXAMPLES

The following examples are included for illustrative purposes only andare not intended to limit the scope of the claimed invention. Unlessotherwise stated, all percentages and parts are on a weight basis.

Preparation of Toughener A

A 6000 (Mw) molecular weight trifunctional polyether polyol(polypropylene oxide based) is poured into a vessel. 11.1 g ofhexamethylene diisocyanate is added and the mixture is heated up to 60°C. Then 0.02 g dibutyltin-dilaurate is added. An exothermic reactionstarts, and the temperature increases up to 80-90° C. Stirring iscontinued until reaction is completed. After the mixture is cooled downto 60° C., 13.5 g 2-allylphenol is added. The solution is stirred at 80°C. for 30 minutes.

Preparation of Toughener B

66.6 g of Polytetrahydrofuran having a molecular weight of approx. 2000(Mw) are preheated at 90° C. The resulting liquid is then poured into avessel and 20.7 g of bisphenol A and 0.3 g of trimethylolpropane areadded. The resulting suspension is heated up to 140° C. and stirreduntil all bisphenol A is dissolved. After the mixture is cooled down to60° C., 12.3 g hexamethylene diisocyanate are added. The mixture isstirred to homogeneity. Then 0.02 g dibutyltin-dilaurate is added. Anexothermic reaction is starting, followed by an increase of temperaturebetween 20 and 30° C. up to 90° C. The solution is cooled and stirredfor 1 hour to finish the reaction.

Preparation of Toughener C

64.2 g of a 6000 (Mw) molecular weight trifunctional polyether polyol(polypropylene oxide based) is poured into a vessel. 9.5 g ofhexamethylene diisocyanate is added, and the mixture is heated up to 60°C. Then 0.02 g dibutyltin-dilaurate is added. An exothermic reactionstarts, and the temperature increases up to 80-90° C. Stirring iscontinued until reaction is completed. The mixture is cooled down to 60°C. and 26.3 g 3-(n-penta-8′-decenyl)phenol is added. The solution isstirred at 80° C. for 30 minutes.

Preparation of the Adhesive

12.5 elastomer modified bisphenol F based epoxy prepolymer, 53.6 g adiglycidyl ether of bisphenol A liquid epoxy resin having an epoxyequivalent weight of approx. 360 (Mw), 12.5 g toughener A, B, or C, aremixed in a laboratory planetary mixture at room temperature for 30minutes. Then 1.2 g Glycidyl ester of a saturated mono carboxylic acid,0.7 g glycidyl silyl ether are added and the mixture is stirred at roomtemperature for another 30 minutes. Then 9.9 g of surface modified fumedsilica and 2.9 g polyvinyl butyral are added and stirred at roomtemperature for 15 minutes. At the end 5.7 g dicyanamide and 0.6 g ofTris(2,4,6-dimethylaminomethyl)phenol in a polymeric matrix are added,and the mixture is stirred for 10 minutes at room temperature. Allmixing steps are performed under vacuum.

The adhesive compositions prepared were tested for a variety ofproperties. Those tests were: lap shear strength (1.5 mm CRS 1403, oil5103S) according DIN EN 1465, impact peel strength (1.0 mm CRS 1403, oil5103S) according ISO 11343, Young modulus, elongation and shear strengthaccording DIN EN ISO 527-1.

The results of the testing on the inventive products and comparativeproducts are included in the following table.

Toughener Standard Toughener Toughener Toughener Toughener¹ A B C Mw72200 51000 49900 34500 Mn 32400 24300 25600 31200 polydispersity 2.22.1 1.9 1.1 Viscosity at 40° 900 60 610 9 C. [Pas] Viscosity at 60° 24020 180 3 C. [Pas] Viscosity at 80° 80 10 60 1 C. [Pas]

Standard Toughener Toughener Toughener Formulation with: Toughener A B CLap Shear strength 28 28 26 27 [MPa] Impact Peel Strength 41 29 39 30[N/mm] Young Modulus [MPa] 1600 2100 2200 2100 Tensile strength [MPa] 3247 51 47 Elongation [%] approx. 10 9 9 6 Viscosity [Pas] 200 30 20 YieldStress [Pa] 80 480 460 ¹Refers to an adhesive as prepared using RAM 965toughener available from Vantico made according to Example 16 ofMülhaupt U.S. Pat. No. 5,278,257.

Adhesives using tougheners B and C of the invention were tested forstreaming on an Intec machine at the following speeds: 150-400 mm persecond using a temperature at the nozzle of 40-65° C. and a pressure offrom about 50 to about 200 bar. The thread behavior and squeezabilitywere judged to be excellent. The adhesives were applied in a bead of 15mm×0.4 mm size to a metal substrate.

1. A method of applying an adhesive composition comprising applying astream of the adhesive composition to a substrate at a speed of fromabout 200 to about 500 mm/s, wherein the adhesive composition comprises,A. one or more epoxy resins; B. one or more rubber modified epoxyresins; C. one or more toughening compositions comprising the reactionproduct of one or more isocyanate terminated prepolymers and one or morecapping compounds having one or more bisphenolic, phenolic, benzylalcohol, aminophenyl or, benzylamino moieties wherein the reactionproduct is terminated with the capping compound; D. one or more curingagents and one or more catalysts for epoxy resins which initiates cureat a temperature of about 100° C. or greater; and E. optionally;fillers, adhesion promoters, wetting agents and rheological additivesuseful in epoxy adhesive compositions; wherein the adhesive compositionhas a viscosity at 45° C. of about 20 Pa·s to about 400 Pa.
 2. A methodaccording to claim 1 wherein the toughening agent has a crosslinkdensity of about 2 or less.
 3. A method of claim 1 wherein the cappingcompound corresponds to the formula

wherein R₄ is a direct bond or an alkylene, carbonyl, oxygen,carboxyloxy or amido moiety; R₅ is independently in each occurrence analkyl, alkenyl, alkyloxy or aryloxy moiety with the proviso that if p=1then q=0; X is O or —NR⁶ with the proviso that X is O where p is 1; andthat where p is 0, X is O in at least one occurrence; o is independentlyin each occurrence 0 or 1 if p is 0, and 0 if p is 1; p is independentlyin each occurrence 0 or 1; and q is independently in each occurrence anumber of from 0 to
 1. 4. A method according to claim 1 wherein thebisphenolic, phenolic, benzyl alcohol, aminophenyl or, benzylaminomoieties of the capping compound contains one aromatic moiety and onealiphatic substituent on the aromatic ring which does not interfere inthe reaction of the amino or hydroxyl groups with an isocyanate groups.5. The method according to claim 4 wherein the isocyanate terminatedprepolymer corresponds to one of the formulas

wherein R¹ is independently in each occurrence a C₂₋₂₀m valent alkylmoiety; R² is independently in each occurrence a polyether chain; R³ isindependently in each occurrence an alkylene, cycloalkylene or mixedalkylene and cycloalkylene moiety; X is O or —NR⁶ with the proviso thatX is O where p is 1; and that where p is 0, X is O in at least oneoccurrence; R⁶ is independently in each occurrence hydrogen or alkyl; mis independently in each occurrence a number of 1 to 6; and n isindependently in each occurrence a number of 1 or greater.
 6. Acomposition according to claim 1 wherein the toughening compositioncorresponds to one of the formulas

wherein R¹ is independently in each occurrence a C₂₋₂₀m valent alkylmoiety; R² is independently in each occurrence a polyether chain; R³ isindependently in each occurrence an alkylene, cycloalkylene or mixedalkylene and cycloalkylene moiety, optionally containing one or moreoxygen or sulfur atoms; R⁴ is a direct bond or an alkylene, carbonyl,oxygen, carboxyloxy, or amido moiety; R⁵ is independently in eachoccurrence an alkyl, alkenyl, alkyloxy or aryloxy moiety with theproviso that if p=1 then q=0; X is O or —NR⁶ with the proviso that X isO where p is 1; that where p is 0, X is O in at least one occurrence; R⁶is independently in each occurrence hydrogen or alkyl; m isindependently in each occurrence a number of about 1 to about 6; n isindependently in each occurrence a number of 1 or greater; o isindependently in each occurrence 0 or 1 if p is 0, and 0 if p is 1; p isindependently in each occurrence 0 or 1; and q is independently in eachoccurrence a number of from 0 to
 1. 7. A method according to claim 6wherein R¹ is independently in each occurrence a 2 to 3 valent C₂₋₈alkyl moiety; R² is a polyalkylene polyether chain having a weightaverage molecular weight of about 400 to about 4000; R³ is independentlyin each occurrence a C₁₋₂₀ alkylene, cycloalkylene or mixed alkylene andcycloalkylene moiety; R⁴ is a C₁₋₂₀ straight or branched chain alkylenemoiety; R⁵ is independently in each occurrence C₁₋₂₀ alkyl, C₂₋₂₀alkenyl, C₁₋₂₀ alkoxy or C-₆₋₂₀ aryloxy moiety with the proviso thatwhere p is 0, R⁵ is a C₁₋₂₀ alkyl moiety; R⁶ is independently in eachoccurrence hydrogen or C₁₋₄ alkyl moiety; m is independently in eachoccurrence about 2 to about 4; n is independently in each occurrenceabout 1 to about 3; p is independently in each occurrence a number of 0or 1 and q is 0 or
 1. 8. A method according to claim 2 wherein theadhesive demonstrates a viscosity of about 30 Pa·s to about 150 Pa·s at45° C.
 9. A method according to claim 8 wherein the adhesive is sprayedas a bead from a nozzle which is located about 3 to about 10 mm from thesubstrate surface.
 10. A method according to claim 8 wherein theadhesive is sprayed using a pressure of about 50 to about 300 bar.
 11. Amethod according to claim 8 wherein the adhesive is sprayed at atemperature of about 20° C. to about 65° C.
 12. A method according toclaim 11 wherein the adhesive is subjected to heating to a temperatureat which the curing agent initiates cure of the adhesive.